Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

VC schreef:
> "Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message
> news:0ssue.127522$jg2.7110724_at_phobos.telenet-ops.be...
> >
> > The expression "for each x in e1 print e2" denotes "[ e2 | x <- e1 ]". Why
> > do you think that apart from this there is some need to give a separate
> > definition of "what print is in DAPLEX"?
>
> OK, let's assume you are right and the expression means what you are saying
> it means, namely e2 is just a copy of e1, nothing more.

?? What do you mean with "e2 is just a copy of e1"? These can be and usually are very different expressions.

> A simple
> experiment would show there is somethng else going in addition to merely
> mapping the original list to its copy.

The list is only mapped to its copy if the function \x.e1 ('\' denoting lambda) is the identity function and that is of course not necessarily true. Perhaps you are confused by the Haskell notation here?

• Jan Hidders